1. Field of the Invention
The present invention relates to a catalyst carrier for a catalytic convertor for purifying an exhaust gas from an internal combustion engine.
2. Description of Related Art
In a conventional catalytic convertor for an internal combustion engine, a catalyst carrier is constructed from a flat metal sheet and a corrugated metal sheet, which are rolled together with their surfaces facing each other so as to form a catalyst carrier of a honeycomb structure. In this construction of the carrier, an improvement for enhancing the exhaust gas purification performance is proposed, wherein the catalyst carrier has, at a middle portion along the length thereof, a means for generation of a turbulent flow of an exhaust gas flowing into the catalyst carrier. Such a turbulent flow allows increased speed in the flow of the exhaust gas, and a higher temperature of the exhaust gas to be maintained so that activation of in middle portion of the catalyst is accelerated. As a result, the commencement of purification of the exhaust gas by the catalyst at the turbulence generator takes place sooner after the engine is started. The heat generated by the reaction at the turbulence generator (a middle part of the catalyst carrier) can enhance activation of the entire catalyst carrier.
In the prior art construction of the carrier, introduction of exhaust gas to a turbulence generator takes place after the exhaust gas passes through a portion of the honeycomb structure located upstream from the turbulence generator whereat the speed of the exhaust gas is slowed down. As a result, a substantial part of a heat carried by the exhaust gas is dissipated prior to the arrival of the exhaust gas at the turbulence generator in the middle part of the catalyst carrier. As a result, the temperature of the exhaust gas at the turbulence generator is low, and, therefore, the speed of activation of the catalyst at the turbulence generator is decreased. In order to suppress the temperature drop of the exhaust gas introduced into the turbulence generator, the turbulence generator can be located nearer to the inlet of the catalyst carrier. However, this solution reduces the length of the honeycomb structure at the inlet end of the catalyst carrier, thereby reducing the mechanical strength of the catalyst carrier.